Electrochemical hydrogen storage performance of Mg–Ti–Zr–Ni alloys

Mg_1.5Ti_0.5−xZr_xNi (x = 0, 0.1, 0.2, 0.3, 0.4), Mg_1.5Ti_0.3Zr_0.1Pd_0.1Ni and Mg_1.5Ti_0.3Zr_0.1Co_0.1Ni alloys were synthesized by mechanical alloying and their electrochemical hydrogen storage characteristics were investigated. X-ray diffraction studies showed that all the replacement elements (Ti, Zr, Pd and Co) perfectly dissolved in the amorphous phase and Zr facilitated the amorphization of the alloys. When the Zr/Ti ratio was kept at 1/4 (Mg_1.5Ti_0.4Zr_0.1Ni alloy), the initial discharge capacity of the alloy increased slightly at all the ball milling durations. The further increase in the Zr/Ti ratio resulted in reduction in the initial discharge capacity of the alloys. The presence of Zr in the Ti-including Mg-based alloys improved the cyclic stability of the alloys. This action of Zr was attributed to the less stable and more porous characteristics of the barrier hydroxide layer in the presence of Zr due to the selective dissolution of the disseminated Zr-oxides throughout the hydroxide layer on the alloy surface. Unlike Co, the addition of Pd into the Mg–Ti–Zr–Ni type alloy improved the alloy performance significantly. The positive contribution of Pd was assumed to arise from the facilitated hydrogen diffusion on the electrode surface in the presence of Pd. As the Zr/Ti atomic ratio increased, the charge transfer resistance of the alloy decreased at all the depths of discharges. Co and Pd were observed to increase the charge transfer resistance of the Mg–Ti–Zr–Ni alloys slightly.     

Study on photocatalytic performance for hydrogen evolution over CdS/M-MCM-41 (M = Zr, Ti) composite photocatalysts under visible light illumination

A series of CdS/M(x)-MCM-41 (M = Zr, Ti, x stands for molar ratio of M/Si) photocatalysts were preprared by hydrotherm, ion-exchange and sulfidation process. The catalysts were characterized by X-ray diffraction, UV-vis spectra and N₂ adsorption-desorption isotherm et al. The characterization results shown that Zr or Ti was successfully doped into the mesoporous of MCM-41, and CdS was also successfully incorporated into such modified mesoporous. The results of photocatalytic performance for hydrogen production shown that CdS/Zr(0.005)-MCM-41 and CdS/Ti(0.02)-MCM-41 had the highest hydrogen evolution activity in triethanolamine aqueous solution under visible light (λ > 430 nm) irradiation, which can be explained by the diffusion velocity of the reactants and resultants and the protection which MCM-41 provided for CdS.     

Optimization of CO2 reforming of methane process for the syngas production over Ni–Ce/TiO2–ZrO2 catalyst using the Taguchi method

In the present study, Taguchi method-based design of experiment with L9 orthogonal array was implemented to optimize the process conditions for CO₂ reforming of methane over the Ni–Ce/TiO₂–ZrO₂ catalyst. The catalyst composition, catalyst reduction temperature, reaction operating temperature, and the CO₂/CH₄ ratio of the reactant gas were the control parameters. The performance index was considered as the response of the Taguchi experiment. The performance index was calculated by considering the product gas H₂/CO ratio, deactivation factor, carbon deposition, and maximum CH₄ conversion. The catalysts were prepared in two steps using the evaporation-induced self-assembly and urea deposition-precipitation methods. The catalysts were characterized in their fresh and spent stages using various techniques like X-ray diffraction, N₂-physisorption, H₂ temperature-programmed reduction, inductively coupled plasma-mass spectroscopy, Scanning electron spectroscopy, Transmission electron spectroscopy, and Thermogravimetric analysis. The results showed that the operating temperature had the principal effect on the performance index. The optimal conditions from signal/noise ratio analysis were Cat3 catalyst with Ti/Zr ratio of 1:3, catalyst reduction temperature of 600 °C, the operating temperature of 800 °C, and feed gas ratio as CO₂/CH₄ = 2. Higher Zr content in the catalyst support and the lower reduction temperature favor enhancing the performance index.     

部分痕量元素在油页岩中的富集特性及挥发行为

选取吉林桦甸、广东茂名、吉林汪清、辽宁大平4个矿区的油页岩为研究对象,用电感耦合等离子发射光谱技术和原子荧光技术对油页岩中14种痕量元素的含量进行了测定.结果表明,油页岩中的痕量元素含量明显高于中国煤中对应元素的平均含量,特别是Mn、P、Ti.与国外煤相比,痕量元素As、Mn、Zn、V、Cu和Cr在我国桦甸油页岩中表现出高含量特性.与地壳丰度相比,油页岩中痕量元素具有比较明显的富集亲硫元素、贫亲铁和亲石元素的特征.同时,研究了燃烧温度对油页岩中痕量元素的挥发行为的影响.结果表明:所研究元素的挥发性均随燃烧温度的升高而增大,其中As、Pb和Zn表现出较强的挥发行为,茂名油页岩中的痕量元素在燃烧过程中表现出较高的稳定性.     

Investigation on synthesis,characterization and hydrogenation behaviour of hydrogen storage material: Fe1−xZrxTi1.3 (x = 0.2)

The present study is aimed at investigations on the structural and microstructural characterization and hydrogenation behaviour of Zr substituted Fe_1−xZr_xTi_1.3 (x = 0.2) alloys. This storage alloy has been synthesized using R.F.induction melting under an argon atmosphere in a previously outgassed graphite crucible. The structural characterization (XRD) has revealed that the as-synthesized sample is multiphasic in nature and embodies the phases FeTi, Fe₂Ti, FeTi₂ and Ti. Microstructural evaluations (SEM) exhibited the presence of interfaces and cracking. The P–C isotherm was determined and it showed the storage capacity of ∼1.20 wt.% at 200°C. The activation as well as desorption kinetics (75% desorption of H₂ in 6 min) were found to be better for Zr-substituted alloy (Fe_0.8Zr_0.2Ti_1.3) as compared to FeTi_1.3. The improved activation and desorption kinetics are thought to be due to presence of several interfaces e.g. Fe(Zr)Ti⧸ Fe(Zr)Ti₂, Fe(Zr)Ti⧸{Fe(Zr)}₂Ti and volume expansion induced cracking of Ti.     

空煤比对煤气化过程中痕量元素迁移规律的影响

采用氢化物发生器和原子荧光光谱法联用(HG-AFS)和电感耦合等离子发射光谱法(ICP-AES),测定了常压流化床煤气化产物中As、Cd、Co、Cr、Cu、Mn、Mg、Ni、Hg、Pb、V、Se、Sr、Zn 14种痕量元素含量,分析了空煤比对痕量元素在气化产物中迁移规律的影响。结果表明：在旋风高温焦中,CA、Ni富集,As、Co、Cu、V、Se、Hg耗散;空煤比对Mn、Sr、Hg、Se、As影响不大;随着空煤比增加,Pb、Zn、Cu、Co、Ni的相时富集系数(REs)略微增加,Cd、Mg的REs减少;V、Cr在低空煤比条件下有较高的REs。在布袋低温焦中,Cd、As、Cu、Cr、Ni、Pb、Zn富集,Co、V、Se、Hg耗散;随着空煤比增加,Pb、Cu、Ni的REs增加;Cd、As、Cr、Se的REs减少。底渣中的Mn和Sr相对于高、低温焦而言有轻微的富集。随着空煤比增加,Cu、Zn在煤气中含量增加,Cr、Co、As、Hg在煤气中含量减小。     

Preliminary study of trace element emissions and control during coal combustion

Hazardous trace element emissions have caused serious harm to human health in China. Several typical high-toxic trace element coals were collected from different districts and were used to investigate the emission characteristics of toxic trace elements (As, Se, Cr, Hg) and to explore preliminary control methods. Coal combustion tests were conducted in several bench-scale furnaces including drop tube furnace (DTF), circulating fluidized bed (CFB) combustion furnace, and fixed-bed combustion furnace. Calcium oxide was used to control the emission of arsenic and selenium. The granular activated carbons (AC) and activated-carbon fibers (ACF) were used to remove mercury in the flue gas from coal combustion. The chemical composition and trace element contents of ash and particulate matter (PM) were determined by X-ray fluorescence (XRF) spectrometry and inductively coupled plasma-atomic emission spectrometry (ICP-AES), respectively. The speciation and concentration of mercury were investigated using the Ontario-Hydro method. X-ray diffraction spectrometry (XRD) was used to determine the mineral composition of production during combustion experiments. With the addition of a calcium-based sorbent, arsenic concentration in PM₁ sharply decreased from 0.25–0.11 mg/m³. In fixed-bed combustion of coal, the retention rates of selenium volatiles were between 11.6% and 50.7% using lime. In the circulating fluidized-bed combustion of coal, the content of selenium in ash from the chimney was reduced to one-fourth of its original value and that in leaching water from the chimney decreased by two orders of magnitude using lime. Calcium-based sorbent is an effective additive to control the emission of As and Se during coal combustion. The emission of chromium is influenced by the occurrence mode of Cr in coal. Chromium emission in PM_2.5 during coal combustion is 55.5 and 34.7 μg/m³ for Shenbei coal and mixed Pingdingshan coal, respectively. The adsorptive capacity of granular activated carbon for Hg⁰ is significantly enhanced through ZnCl₂-impregnation. The activated carbon fibers showed decent efficiency in mercury adsorption, on which surface oxygen complex showed positive effects on mercury adsorption.     

COx-free hydrogen generation via decomposition of ammonia over al,Ti and Zr−Laponite supported MoS2 catalysts

There is a need for more efficient, stable and cost-effective catalytic support for efficient catalysts to meet the increasing demand for large production and transportation of hydrogen energy. Laponite RD, a synthetic clay mineral was used to prepare Al, Ti and Zr grafted Laponite by a post grafting method at room temperature (RT). The acid-functionalized Al, Ti and Zr−Laponite were utilized as a support for the preparation of MoS₂ catalyst under the hydrothermal method by a soft chemical approach using thiourea as a sulphur source. Even though it contained almost the same amount of MoS₂, it exhibited enhanced ammonia conversion due to the type of heteroatom influence on the support. Detailed characterization of the catalysts illustrated that MoS₂/Zr−Laponite shows good acidic/basic properties, H₂ desorption properties and reducibility of MoS₂ on the support. Moreover, the support enables a large surface area providing a maximum MoS₂ dispersion. These structural features make MoS₂/Zr−Laponite as a promising catalyst that is cost-effective and requires a simple preparation procedure. Physicochemical properties of the catalyst were characterized by high-angle XRD, N₂ sorption analysis, NH₃, CO₂ and N₂ temperature programmed reduction (TPD), H₂ temperature programmed reduction (TPR) and TPD, HR-TEM, HR-SEM and XPS techniques.     

A preliminary method for determining acceptable trace element levels in coal

A preliminary method for determining acceptable trace element levels in coal was established. In addition to the conventional coal quality parameters ash and sulfur, potentially hazardous trace elements As, Be, Cd, Cl, Cr, F, Hg, Mn, Ni, Pb and Se were selected for the evaluation, and their environmentally acceptable concentrations in coal were quantified at 5 and 0.5 weight %, and 6.5, 1, 0.8, 400, 15, 120, 0.15, 80, 30, 15 and 2.5 mg/kg, respectively. A pollution index (I) is proposed, by which coal is ranked into four classes: acceptable (I ≤ 0.252), marginal (0.252 < I ≤ 0.514), unacceptable (0.514 < I ≤ 0.751), and ultra-unacceptable coal (I > 0.751). 36 coal samples collected from the north of Ordos basin and Shanxi Province, China were classified with the method. Most of the cleaned coals were rated as acceptable or marginal, while the run-in-mine coals, feed coals, middlings and coal slimes were generally ranked as unacceptable or ultra-unacceptable coal. The evaluation results reflect the degree of cleanliness of these coal samples.     

Improvement of hydrogen storage properties of TiCrV alloy by Zr substitution for Ti

The effects of Zr substitution for Ti on the hydrogen absorption–desorption characteristics of Ti_1−xZr_xCrV alloys (x = 0, 0.05, 0.1 and 1.0) have been investigated. The crystal structure, maximum hydrogen absorption capacity, kinetics and hydrogen desorption properties have been studied in detail. While TiCrV crystallizes in body centered cubic (BCC) structure, ZrCrV is a C15 cubic Laves phase compound and the intermediate compositions with 5 and 10 at% Zr substitutions for Ti (x = 0.05 and 0.1) show the presence of a small amount of ZrCr₂ Laves phase along with the main BCC phase. The pressure–composition isotherms have been studied at room temperature. TiCrV shows separation of TiH₂ phase on cycling. A small amount of Zr substitution for Ti is found to have advantageous effects on the hydrogen absorption properties of TiCrV as it suppresses TiH₂ phase separation and decreases hysteresis. It is found that the hydrogen absorption capacity of Ti_1−xZr_xCrV decreases as the Zr content increases due to the increased fraction of Laves phase. Temperature-programmed desorption studies have been carried out on the saturated hydrides in order to find the relative desorption temperatures.     

EXAFS and SAXS studies of ZrCo alloy doped with Hf,Sc and Ti atoms

The local structures of ZrCo alloy doped with Hf, Sc and Ti atoms before and after hydrogenation were studied by extended X-ray absorption fine structure (EXAFS) technique. For all the samples, the length of the Co–Zr bond increased and the coordination numbers of Co reduced after hydrogenation. As the Hf, Sc and Ti atoms came into the ZrCo alloy, the lengths of the Co–Zr bond varied. The ingoing Ti atoms had shortened the Co–Zr bond lengths from 2.74 to 2.62 Å in the pre-hydrogenation, whereas all of the doped atoms had no obvious effect in the post-hydrogenation. Also the size distribution of the nanoparticles in the as-cast and hydrogenated Zr–Co alloy was investigated by small-angle X-ray scattering (SAXS) technique.     

Structural characterization and electrochemical hydrogen storage properties of Ti2−xZrxNi (x = 0, 0.1, 0.2) alloys prepared by mechanical alloying

Nominal Ti₂Ni was synthesized under argon atmosphere at room temperature using a planetary high-energy ball mill. The effect of milling time and Zr substitution for Ti on the microstructure was characterized by XRD, SEM and TEM, and the discharge capacities of Ti_2−xZr_xNi (x = 0, 0.1, 0.2) were examined by electrochemical measurements at galvanostatic conditions. XRD analysis shows that amorphous phase of Ti₂Ni can be elaborated by 60 h of milling, whereas Zr substitution hinders amorphization process of the system. The products of ball milling nominal Ti_2−xZr_xNi (x = 0.1, 0.2) were austenitic (Ti, Zr)Ni and partly TiO, despite the fact that the operation was carried out under argon atmosphere. By comparing the SEM micrographs, it is found that the amorphous phase of Ti₂Ni was formed in the stage of cold-welding during milling, while with Zr substitution particles were flaky and finer, inhomogeneous in size distribution with massive agglomeration. TEM analysis was carried out and confirmed the observations via XRD. In the electrochemical tests, amorphous Ti₂Ni shows the best discharge capacity at 102 mAh/g at a current density of 40 mA/g. Without need of activation, it exhibits extraordinary cycling stability under room temperature. On the other hand, the effect of Zr substitution on the electrochemical property of Ti₂Ni is tricky, as superficially the discharge capacity drops drastically with Zr substitution, but with increase of Zr content (from x = 0.1 to x = 0.2), the discharge capacity increases generally, which credits to larger unit-cell-volume provided by ZrNi compared to TiNi. It is also found that the Ti–Ni system becomes significantly susceptible to oxidation when Zr is introduced to the initial powders as mechanical alloying is deployed as a synthesis method.     

DFT study of crystal structure and electronic properties of metal-doped AlH3 polymorphs

AlH₃ has been considered for a long time as a hydrogen storage material with suitable gravimetric and volumetric density for practical applications. Among eight AlH₃ polymorphs observed so far, in this work we focus our attention on an investigation of the effects of various metal dopants in α- and β-AlH₃, to perceive a way of enhancing them. Substitutional incorporation of the metal dopants (Li, Sc, Ti, Cu, Cr, Fe, Nb, Mo, Zn, or Zr) is considered, as well as interstitial doping with Li, Sc, Ti, Cu, and Zr. The density functional theory (DFT) (using GGA-PW91) approach is used to address the crystal structure, bonding, dopant stability, and changes in hydrogen desorption energy. In addition, the kinetics of hydrogen desorption is also considered for several interstitially doped cases, by calculating the stability of native point defects. Promising results are presented for Zr, Ti, and Sc – doped hydrides. Doped hydrides, here studied, are considered as n- or p-type semiconducting materials, enabling wider application overcoming hydrogen storage scope.     

Superior anti-impurity gas poisoning ability and hydrogen storage properties of Ti–Cr alloy by introducing zirconium as additive

In this work, the anti-impurity gas poisoning ability and hydrogen storage properties of Ti–Cr alloy by introducing zirconium as additive have been investigated. The results showed that all alloys had C14-type main phase and Ti minor phase. The lattice parameter a, c and cell volume of the C14-type phase rose as Zr content increased. Furthermore, after introducing Zr, all alloys could absorb hydrogen immediately without any prior heat treatment or hydrogen exposure with/without prolonged air exposure. The maximum hydrogen storage capacity and the average effective hydrogen storage capacity of TiCr₂ alloy also increased with Zr content. The cycle properties of all alloys with/without prolonged air exposure were also discussed. The results showed that all alloys had good cycle stability even if the alloys were exposed to the air for 2 days. The above results suggested that the addition of Zr had a positive effect on improving the hydrogen storage properties and anti-impurity gas poisoning properties of TiCr₂ alloy. Finally, the mechanisms of first hydrogenation kinetic of all alloys with/without prolonged air exposure were also investigated by using the rate limiting step.     

Energy from municipal solid waste: A comparison with coal combustion technology

The conversion of municipal solid waste (MSW) to energy can conserve more valuable fuels and improve the environment by lessening the amount of waste that must be landfilled and by conserving energy and natural resources. The importance of utilizing MSW was recognized in the 1991 U.S. National Energy Strategy, which sought to “support the conversion of municipal solid waste to energy.” One route to utilizing the energy value of MSW is to burn it in a steam power plant to generate electricity. Coal has long been the predominant source of energy for electricity production in the U.S.; therefore, a considerable science and technology base related to coal combustion and emissions control can be, and has been, applied with substantial benefit to MSW combustion. This paper compares the combustion of coal and MSW in terms of fuel characteristics, combustion technology, emissions, and ash utilization/disposal. Co-combustion of coal and MSW is also discussed. MSW issues that can be addressed by research and development are provided.The major environmental issues that designers of MSW combustion systems have had to address are emissions of trace organic compounds, particularly polychlorinated dioxins and furans, and trace elements such as mercury, lead, and cadmium. Emission of trace organics is generally the result of a poorly designed and/or operated combustion system; modern MSW systems use good combustion practices that destroy organic compounds during the combustion process. Proper control of air/fuel mixing and temperature, and avoidance of “quench” zones in the furnace, help to ensure that potentially harmful organics are not emitted. Computer codes and other design and troubleshooting tools that were developed for coal combustion systems have been applied to improve the performance of waste-to-energy systems.Trace element emissions from both coal and MSW combustion result primarily from vaporization of elements during the combustion process. Most of the trace elements that are vaporized condense on fly ash as the combustion products cool downstream of the furnace and can be effectively controlled by using an efficient particulate removal device. However, volatile elements, particularly mercury, are emitted as a vapor. Several mechanisms are available to capture mercury vapor and some are in use. The development of satisfactory control technology for mercury is a topic currently of high interest in coal burning.The potential for leaching of trace elements and organics from MSW residues after disposal raises issues about the classification and management of ash. Results of laboratory leaching tests, especially for lead and cadmium, have not been consistently supported by field experience. Careful interpretation of the available test protocols is needed to make sure that residues are properly managed.Because of the large scale of coal-fired boilers for electricity production, co-firing of MSW with coal in such boilers could consume large quantities of waste. Several short-term demonstrations have shown that co-firing is feasible. The issues involved in co-firing are emissions of trace elements, trace organics, and acid gases; boiler slagging and fouling; and long-term effects, such as corrosion and erosion of boiler tubes.Areas where research and development has contributed to improved MSW combustion include (a) the formation mechanisms of polychlorinated dioxins/furans, especially low-temperature, catalytic mechanisms, (b) methods of combustion air distribution in incinerators that result in better combustion and reduced emission of organic compounds, (c) the use of gas reburning to control NOx and reduce emission of organic compounds, (d) practical methods for removing organic compounds and mercury from MSW flue gas, (e) the performance of electrostatic precipitators in removing MSW fly ash, particularly when co-firing MSW and coal in existing coal-fired boilers, and (f) burning MSW in fluidized beds or of pulverizing refuse-derived fuel and firing it in suspension-fired, pulverized coal boilers.     

Exploration of Ti substitution in AB2-type YZrFe based hydrogen storage alloys

To improve the hydrogen storage properties of YZrFe alloys, the alloying with Ti was carried out to obtain Y_0.7Zr_(0.3-x)Ti_xFe₂ (x = 0.03, 0.09, 0.1, 0.2) alloys by different processes. It was expected that Ti would substitute Zr and decrease the lattice constant of YFe₂-based C15 Laves phase. All YZrTiFe quaternary alloys consist of the main Y(Zr)Fe₂ phase and the minor YFe₃ phase. Despite the large solubility of Ti in Zr or Zr in Y, the Ti incorporation into YZrFe alloys results in the inhomogeneity of Y and the segregation of Ti, and thus decreases the hydrogen storage capacity. Only the alloy Y_0.7Zr_0.27Ti_0.03Fe₂ containing very few Ti shows the substitution of Ti to Zr and the resultant improvement in the dehydriding equilibrium pressure.     

Element mobility during the hydrothermal alteration of rhyolitic rocks of the Los Azufres geothermal field, Mexico

The effects of hydrothermal alteration on major, rare-earth, and other trace-element concentrations in rhyolitic rocks of the Los Azufres geothermal field, Mexico, were investigated by statistically comparing the chemical compositions of altered drill cuttings (taken above 450 m depth) with those of fresh rock outcrop samples. Altered rhyolitic rocks show predominantly vitreous and fluidal textures, with alteration products (mainly clay minerals, chlorites and, less commonly, sericite) comprising up to 40% of the rock mass; cryptocrystalline quartz, chlorite, and zeolites fill fractures and vesicles. In altered rocks the greater statistical variances of several elements (Y, Ce, Pr, Nd, Sm, Lu, and Pb) are probably due to alteration effects, whereas smaller variances for CaO, Sr, Rb/Sr, and Rb/Ba suggest that alteration processes have resulted in more uniform chemical compositions. Only MnO, P₂O₅, Ta, Zr, and Nb have significantly different concentrations in hydrothermal altered rocks as compared to fresh rocks. MnO, P₂O₅, Ta, Rb/Zr, and Rb/Nb decrease, whereas Zr, Nb, and Nb/Y increase in the altered rocks. The present study stresses that caution should be taken when using these chemical parameters for petrogenetic studies of old hydrothermally altered areas, particularly with rhyolitic rocks. Rare-earth element (REE) concentrations were not significantly different between fresh and altered rhyolitic rocks. This may indicate that these elements were relatively immobile during the hydrothermal alteration processes affecting the rhyolites at Los Azufres, or more likely that they were reincorporated into hydrothermal minerals after being mobilized from the primary phases.     

Catalytic activity of SBA-15 supported Ni catalyst in CH4 dry reforming: Effect of Al,Zr, and Ti co-impregnation and Al incorporation to SBA-15

In this study, the catalytic activity of the mesoporous SBA-15 supported Ni–Al, Ni–Zr, and Ni–Ti catalysts prepared by an impregnation method were investigated in dry reforming of methane. In addition, Al incorporated SBA-15 (Al–SBA-15) materials used as catalyst support were synthesized following a one-pot hydrothermal route in three different conditions: synthesis in the presence of only HCl, only NaCl, and both HCl and NaCl (denoted as A, S, and B, respectively). All catalysts were characterized by XRD, N₂ adsorption-desorption isotherms, ICP-OES, DRIFTS, SEM, TEM-EDX and TGA techniques before and/or after reaction tests. Among Al, Zr, and Ti impregnated catalysts, Ni–Al impregnated catalyst showed the highest activity in dry reforming of methane. According to activity test results, Al–SBA-15 supported Ni catalyst prepared by the one-pot hydrothermal route in the presence of both HCl and NaCl showed the best catalytic activity with high methane (81%) and carbon dioxide conversion (88%) values at 750 °C. The highest H₂ and CO selectivity values were obtained with the same catalyst with an H₂/CO molar ratio of 0.80. Therefore, these results showed that partial Al (0.11%) incorporated into the structure of SBA-15 was sufficient to improve the catalytic activity of the catalyst in dry reforming of methane.     

Improvement of hydrogen storage properties of Mg by catalytic effect of Al-containing phases in Mg-Al-Ti-Zr-C powders

The hydrogen storage (HS) properties and structures of ball-milled (BM) Mg-Ti-Al-Zr-C powders prepared under various milling conditions were investigated. The additions Ti, Zr, Al and C improved HS performance of Mg-based materials. The beneficial effect can be explained by catalysis of particles rich in Al, Ti and Zr located on the surface of Mg grains. The particles provide effective pathways for the hydrogen diffusion from/into the re/forming MgH₂. The morphological and microstructural characteristics were investigated by scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM) and by X-ray diffraction (XRD). The hydrogen sorption was measured by Sieverts method. The various preparation processes of powders resulted in two phases: Mg₁₇Al₁₂, Mg_1.95Al_0.05. It was found, that mainly these phases had a strong positive effect on HS properties of studied powders. Both phases increased desorption/absorption equilibrium pressure. Improvement of desorption kinetics of powder containing phase Mg₁₇Al₁₂ was more expressive than powders with of Mg_1.95Al_0.05.     

Ni–B and Zr–Ni–B in-situ catalytic performance for hydrogen generation from sodium borohydride,ammonia borane and their mixtures

In this study, the parameters on the catalytic hydrolysis of the sodium borohydride (NaBH4, SBH) and ammonia boranes (NH3BH3, AB) mixtures were investigated such as the effect of Zr additive in the catalyst, using in-situ or powder catalysts, the molar ratio of the SBH/AB mixture (2, 4, 8, neat SBH, neat AB) and temperature. As the catalyst, in-situ synthesized Ni–B and Zr–Ni–B for the first time were used to produce H₂ from hydrolysis of the SBH and AB mixtures. The SBH and AB mixtures were used to determine provided or not an effect on reaction. Catalyst preparation and hydrolysis reactions took place in the same reactor spontaneously for in-situ works. The Zr–Ni–B catalyst gives better results than Ni–B and increases efficiency at 25 °C and 35 °C temperature. When Zr–Ni–B catalyst compared experimentally among themselves, the best yield result at 45 °C temperature, for neat SBH, mole ratio in 4 and mole ratio in 8, as 87%, 86% and 83% respectively. For hydrolysis reactions with Zr–Ni–B catalyst, activation energies of SBH and AB were calculated as 45.23 kJ/mol and 79.76 kJ/mol, respectively. SEM, BET, XPS analyzes have been used to characterize these catalysts. The addition of Zr provided increase effect on the surface area. The surface area increases from 44.33 m²/g to 175.50 m²/g.